A wireless portable Internet (i.e., wireless broadband (WiBro) or a high-speed portable Internet) is a next-generation communication system that supports mobility to local data communication methods such as the conventional wireless LAN using a fixed access point.
FIG. 1 is a schematic diagram of a wireless portable Internet system.
As shown in FIG. 1, a wireless portable Internet system includes a portable subscriber station (PSS) 110, a radio access station (RAS) 120, an access control router (ACR) 130, an Internet protocol (IP) network 140, a home agent (HA) 150, an authentication, authorization, and accounting (AAA) server 160, and an Internet 170.
The PSS 110 uses high-speed wireless Internet services by accessing the wireless portable Internet system and receiving/transmitting traffic data, and performs a low-power radio frequency (RF)/intermediate frequency (IF) module and controller function, a function of control variation of a media access control (MAC) frame according to service characteristics and propagation environment, a hand-off function, and an authentication and encryption function.
As a base station of the wireless portable Internet system, the RAS 120 wirelessly transmits data received from the ACR 130 to the PSS 110, and performs a low-power RF/IF module and controller function, an orthogonal frequency division multiplexing access (OFDMA)/time division duplex (TDD) packet scheduling and channel multiplexing function, a function of control variation of a media access control (MAC) frame according to service characteristics and propagation environment, a high-speed traffic real-time control function, and a hand-over function. In addition, the PSS 110 and the RAS 120 respectively have a packet transmission modulation/demodulation function for data transmission, a high-speed packet channel coding function, and a real-time modem control function.
As a packet access router connecting ACRs 120, the ACR 130 includes a plurality of RASs 120 and performs a handover function between the RASs 120 and between ACRs 130, a packet routing function, and an Internet access function, and it accesses the IP network 140.
The IP network 140 is connected with the HA 150 and the AAA server 160, and receives packet data from an external packet data service (i.e., Internet 170) and delivers the received packet data to the ACR 130.
The HA 150 performs routing for transmission of the data to the PSS 110 from the Internet 170 when using a mobile IP, and the AAA server 160 charges the PSS 110 for using data and authenticates access of the PSS 110.
When the PSS 110 transmits uplink data in the wireless portable Internet system, ranging is performed to adjust transmission parameters such as power of the PSS 110, timing, and frequency offset so as to successfully transmit the uplink data to the RAS 120.
The ranging process in the wireless portable Internet is divided into an initial access/handoff ranging process, a periodic ranging process, and bandwidth request ranging using a bandwidth request code.
The initial access/hand-off ranging process is performed for adjusting transmit power, timing, and frequency offset of the PSS 110 and starting an initial signal access process when the PSS 110 initially accesses the RAS 120 or attempts a handoff to the RAS 120.
The periodic ranging process is periodically performed so as to adjust transmit power, timing, and frequency offset of the PSS 110. The transmission parameters vary as the PSS 110 moves.
FIG. 2 is a signal flowchart of the periodic ranging process in the wireless portable Internet system.
The PSS 110 in the wireless portable Internet system determines whether a timer T4 is terminated in order to perform the periodic ranging process. In this case, the timer T4 measures a maximum time interval for at least one allocation of an uplink resource, and checks a periodic ranging interval.
When it is determined in step S210 that the timer T4 is terminated, the PSS 110 transmits a periodic ranging code to the RAS 120, in step S220. In this case, the periodic ranging code is a ranging request signal that is simultaneously transmitted to the RAS 120 from the PSS 110 when the timer T4 is reset so that the timer T4 can perform periodic ranging for every interval of the timer T4.
The RAS 120 adjusts the transmission parameters (e.g., transmit power, timing, and frequency offset) when receiving the periodic ranging code in step S230, and transmits transmission parameter adjustment values to the PSS 110 through a ranging response (RNG_RSP) signal, in step S240.
The PSS 110 adjusts the transmit power, timing, and frequency offset by using the received transmission parameter adjustment values. Such a periodic ranging process is performed for every interval of the timer T4, in step S250.
The ranging process using the bandwidth request code is performed to request a bandwidth for transmission of uplink traffic when the uplink traffic is generated in the PSS 110.
FIG. 3 is a signal flowchart of a bandwidth allocation and ranging process by a bandwidth request code in the wireless portable Internet system.
When uplink traffic is generated in the PSS 110 in step S310, a bandwidth request code is transmitted to the RAS 120 in step S320.
When receiving the bandwidth request code, the RAS 120 generates an RNG_RSP signal including transmission parameter adjustment values (e.g., measured frequency offset, transmit power, and timing) in step S330, and transmits the generated RNG_RSP signal to all PSSs in the RAS 120, in step S340. When receiving the RNG_RSP signal including the transmission parameter adjustment values, the PSS 110 adjusts the transmission parameters (e.g., timing, transmit power, frequency offset) in step S350.
In addition, the RAS 120 transmits code division multiplex access (CDMA) allocation information element (CDMA_Allocation_IE) of an uplink MAP (UL-MAP) in step S360. Herein, the CDMA_Allocation_IE includes an uplink interval usage code (UIUC), a repetition code indicator (RCI), a frame number index, a ranging code, a ranging symbol, a ranging sub-channel, and a bandwidth (BW) request mandatory, and provides radio resource information of the corresponding uplink.
The PSS 110 performs a ranging process through the received CDMA_Allocation_IE, and transmits a bandwidth request header to the RAS 120 by using a bandwidth allocated to the UL-MAP, in step S370. The RAS 120 generates a UL-MAP and an DL-MAP to which bandwidths for uplink traffic transmission of the PSS 110 are allocated through the received bandwidth request header and transmits the UL-MAP and the DL-MAP to the PSS 110 in step S380, and the PSS 110 transmits UL traffic by using the bandwidths allocated to the UL-MAP and DL-MAP, in step S390.
Such a periodic ranging process has a problem of degrading resource use efficiency since the periodic ranging process requires a relatively larger number of ranging channels than the initial access/hand-off ranging process or the bandwidth request ranging. In addition, substantial data transmission timing of the PSS may be delayed even though transmit power is precisely adjusted through the periodic ranging, and accordingly, a power control gain obtained through the periodic ranging may be lower than expected.
In addition, the ranging process using the bandwidth request code as shown in FIG. 3 also causes a delay in uplink traffic transmission since a delay occurs in the receiving of an RNG_RSP message and the processing of the RNG_RSP until the PSS transmits a bandwidth request code and the RAS transmits a bandwidth request header.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.